Delta(U) = Cvdelta(T) for Ideal Gases?

[Lairix]

I don't understand how Delta(U) = Cvdelta(T) is always true for Ideal Gases...Shouldn't this only be true for constant volume processes? Yet it seems to be used even when a gas is expanding or being compressed...

Any ideas...Thanks in advance.

 

[Astronuc]

This lecture explains it in a sequence of constant volume + constant pressure steps
http://pruffle.mit.edu/3.00/Lecture_11_web/node1.html

 

[Chestermiller]

I don't understand how Delta(U) = Cvdelta(T) is always true for Ideal Gases...Shouldn't this only be true for constant volume processes? Yet it seems to be used even when a gas is expanding or being compressed...

Any ideas...Thanks in advance.

The internal energy of an ideal gas is a function only of temperature. We know this because, if you have a real gas at low pressure in half of a rigid container and vacuum in the other half, and you break the seal, after the system has re-equilibrated at a lower pressure, the temperature does not change. This shows that the internal energy does not depend on pressure. A real gas in the limit of low pressures is what we refer to as an ideal gas.

Chet